In recent years, demand has continued to increase for various high-density and high-integration electronic devices that require fine processing, including a semiconductor device. In a semiconductor device production process, a photolithographic process (photolithography) plays an important role in forming a fine pattern. In the photolithography, a technique capable of stably performing fine processing with an accuracy of 100 nm or less is required. For this reason, a resist is also required so that a pattern of 100 nm or less can be formed with accuracy.
As a conventionally popular resist, diazonaphthoquinone-novolak type resists based on a dissolution inhibition effect of a diazonaphthoquinone compound on a phenolic resin material have been known (U.S. Pat. No. 4,859,563).
When a low-molecular weight phenolic resin material is used in the diazonaphthoquinone-novolak type resists, the dissolution inhibition effect of the diazonaphthoquinone compound is not sufficiently achieved, so that a development contrast between an exposed portion and an unexposed portion is low.
Lately, as a resist capable of providing a higher resolution than the diazonaphthoquinone-novolak type resist, a chemically amplified resist has been used. The chemically amplified resist generates an acid (H+) by active ray irradiation and causes a deprotection reaction of an alkali-soluble group protected with an acid-degradable group, thus being solubilized in an alkali (Journal of Photopolymer Science and Technology, 17, 435 (2004)).
When a resist pattern of the chemically amplified resist is prepared, heat treatment is performed before development in order to accelerate the deprotection reaction in the presence of the acid, as a catalyst, generated at the exposed portion.
During the heat treatment, the acid is diffused by heat in a length of approximately 10 nm (“Proc. SPIE”, 6154, 710 (2006)). As a result, line edge roughness (LER), which is minute projections and recesses at an edge portion of the resist pattern, is generated and the acid diffusion leads to a decrease in resolution.
Another factor causing the LER may includes an influence of a molecular weight of a base compound. Herein, the base compound means a compound having an alkali-soluble group or a protected alkali-soluble group in a resist composition.
Dissolution of the base compound in a developing liquid is caused at one molecule unit of the base compound, so that the LER is larger with a large molecular weight.
A lower molecular weight compound has a lower glass transition temperature and a lower melting point. The chemically amplified resist has a long acid diffusion length when the heat treatment before development is performed at a temperature higher than a glass transition temperature thereof, so that a resultant resolution is decreased.
In other words, the base compound for the chemically amplified resist is required to have a glass transition temperature higher than a deprotection reaction temperature in the presence of the acid catalyst. This requirement constitutes a constraint on a lower LER design, i.e., a lower molecular weight design of the chemically amplified resist.